Meander line loaded antennas are known and are exemplified by U.S. Pat. Nos. 5,790,080; 6,313,716; 6,323,814; 6,373,440; 6,373,446; 6,480,158; 6,492,953; 6,404,391 and 6,590,543. These patents are assigned to the assignee hereof and are included herein by reference.
In all of the prior meander line loaded antennas there is a right angle between the horizontal and vertical radiators, with the top plate being parallel to the ground plane plate utilized. This plate configuration optimizes the current distribution for maximum bandwidth.
As illustrated in the above patents, in order to make reduced-sized or miniaturized antennas, a meander line has been utilized to load the antenna in such a manner that the size of the antenna can be diminished while at the same time providing for a relatively wide bandwidth response for the antenna.
As illustrated in U.S. patent application Ser. No. 10/123,787 filed Apr. 16, 2002 entitled “Method and Apparatus for Reducing the Low Frequency Cut-off of a Wideband Meander Line Loaded Antenna” by John T. Apostolos, an L-shaped antenna is provided in which a vertical upstanding plate orthogonal to a ground plane is spaced from a horizontally-extending plate parallel to the ground plane, with the signal to the antenna being applied between the ground plane and the upstanding plate. Here, a capacitive member or cap bridges the slot or gap between the upstanding plate and the horizontal plate. It has been found that the utilization of the capacitor over the gap contributed substantially to the lowering of the low frequency cut-off of the wideband meander line loaded L-shaped antenna.
As with all meander line loaded antennas, a significant cost to the antenna is the provision of the meander line itself, which requires spaced-apart plates or strips which provide for an impedance discontinuity that in effect lengthens the overall size of the antenna while at the same time keeping the antenna small due to the folded meander line configuration. In practice, these meander lines are separately fabricated and are attached to or positioned adjacent the vertical and horizontal plates making up the L-shaped antenna. The separate fabrication of the meander line not only complicates construction of the antenna but also is somewhat costly to manufacture.
When such antennas are to be used, for instance, in cellular phone antennas, or with personal digital assistants or PDAs, it is important that these antennas not only work in the 830 MHz cellular band but also in the PCS bands, either 1.7 GHz or 1.9 GHz. Thus it is important that a single miniature antenna be able to operate effectively in these two bands. More particularly, each of these two bands is subdivided into two bands such that for PDA applications, it is important to have an antenna which has acceptable gain in each of the four bands of operation.
In another application, the so-called ultra-wideband service, these antennas must work from, for instance, 3 GHz to 9 GHz with an acceptable gain across the entire band. This service involves spread spectrum signaling in which miniscule amounts of energy are “smeared out” across the entire band through which the energy is swept. The purpose of the use of ultra-wideband is to make it possible to use bands for which there is already an allocated use. The ultra-wideband transmissions are said to be of such a small magnitude that they do not contribute substantially to interference with the normal signals in these bands.
It is therefore necessary for PDA applications, cellular applications and indeed ultra-wideband applications that a miniaturized antenna be provided which is simple to manufacture and is cost effective. With more than 20 million cell phones currently activated in the United States, the ability to provide new equipment for these cellular and PCS applications requires an extremely simple antenna system which is cost effective to manufacture and can be easily replicated for mass production of such equipment.
Many of the PDAs, cell phones or wireless transceivers are provided in a hand-held package having a clamshell configuration. It is therefore important to be able to provide a wideband antenna which can be housed in the top clamshell that is flipped open to expose an underlying keypad and display.
While in operation the back of such a hand-held device is covered with one's hand, the flipped-up portion of the clamshell is not covered during normal operation. It is therefore important to be able to provide an antenna which is housable in the upper clamshell and which has sufficient gain across the bands of interest so that, for instance, PCS and cellular PDAs can operate in a robust manner.
In the past, for multi-band coverage wireless handset manufacturers have utilized stacked patch antennas, each tuned to a different band and located one on top of the other.
However, such stacking of patch antennas is problematic because the antennas interfere one with the other, thus precluding the requisite gain in each of the four bands. Moreover, in order to get an antenna to operate in ultra-wideband devices between 3 GHz and 9 GHz with sufficient gain over the entire bandwidth, other than meander line loaded antennas, there is presently no miniaturized antenna available for such hand-held units.
While meander line loaded antennas have been suggested for such applications, the cost of the meander line can double the cost of the antenna, which while providing for the requisite characteristics, is a relatively expensive solution.